Export multi-pass .exr image sequence from cycles?
To save all the passes for each frame into a multilayer OpenEXR:

Add an Input>Image Sequence node and use that to import the OpenEXR sequence

Add an Output>File Output Node and set it to Use OpenEXR multilayer and plug the outputs of the Image sequence to it.

You still need a valid output for the render. So create a dummy file, a jpeg file will do. You can erase those later. 



Then just set your frame range and render as animation (ctrl F12)

(and remember to erase the jpeg dummy files)